This project is currently focusing on the hormonal, neural and pharmacological factors underlying vocal expression in nonhuman primates. Major findings this year include: 1. An autoradiographic study of the distribution of oxytocin binding sites in the brains of common marmosets found evidence for oxytocin specificity. Sites binding 125I-oxytocin show significant reduction in binding when co-treated with vasotocin (an oxytocin receptor antagonist), but not when co-treated with a ligand for vasopressin receptors. Further localization of forebrain receptor sites was made, with the most prominent encompassing the nucleus accumbens and olfactory tuberculum. A separate area occurs in the nucleus basalis/lateral amygdala region. 2. Hormonal status of single adult male squirrel monkeys living in proximity to a social group of females is correlated with changes in female vocal behavior. Females living adjacent to a male with high circulating testosterone level for 3 weeks showed a 10-fold increase in purrs and errs over pre-male introduction, whereas females living adjacent to a male with low testosterone level did not exhibit any change in their vocal behavior.